Closed-head polyaxial and monaxial screws

ABSTRACT

A closed-head polyaxial screw for use in spinal instrumentation for spinal fusion, treatment of deformity, or the like. Polyaxial screws may have a two-part design, with the screw fitting into an aperture in the closed head. One or more clamps may secure the bone screw in the aperture. A closed-head polyaxial screw having a one part design is also disclosed. In addition, a one-part monaxial screw is described.

REFERENCE TO RELATED APPLICATIONS

The present application is a continuation application of U.S. patentapplication Ser. No. 15/225,177, filed Aug. 1, 2016 (published as U.S.Pat. Pub. 2016-0338739), which is a continuation application of U.S.patent application Ser. No. 13/409,209, filed Mar. 1, 2012 (now U.S.Pat. No. 9,427,260), all of which are hereby incorporated by referencein its entirety.

BACKGROUND OF THE PRESENT DISCLOSURE 1. Field of the Present Disclosure

The present disclosure is directed to closed-head bone screws forsecuring spinal instrumentation. Both monaxial and polyaxial screws aredescribed.

2. Related Art

Spinal instrumentation may be used to treat a variety of conditions,including injury and deformity due to trauma or congenital defect.Spinal instrumentation may also be used in a spinal fusion procedure toalleviate the difficulties caused by a damaged or herniatedintervertebral disc. Spinal instrumentation typically includes a numberof bone screws for attaching to individual vertebrae. The pedicle is apreferred attachment point because it is easily accessible from the backof the patient and it offers a great depth of cortical bone. Once thepedicle screws are in place, one or more rods are placed vertically,substantially parallel to the long axis of the spine, and connected tothe pedicle screws. Each rod is usually connected to at least twoscrews, each of which is attached to a different vertebra. The entireconstruct serves to properly align and/or separate the vertebrae. It maybe supplemented with bone grafts, bone cement, or the like, to promotehealing, long-term stability, and the like.

Traditionally, spinal instrumentation was installed via open-backsurgery. This type of procedure tended to cause extensive trauma to thepatient, resulting in long and painful recovery times. In recent years,a shift has been made toward minimally invasive surgery techniques. Inminimally invasive surgery, the surgeon makes only one to a few smallincisions and uses special tools to insert devices, observe hisprogress, and perform other activities in the surgical site. Minimallyinvasive surgery techniques frequently result in much less injury to thepatient and improved healing and recovery times.

The pedicle screws commonly used in instrumentation procedures utilizean open-head design to connect to the rods. This head has a flat basewith an arm rising on either side, giving it a U-shaped profile. In amonaxial design, the bone screw itself may be inserted through anopening in the base and then inserted into the bone. The rod is placedbetween the upright portions of the open head, and a locking clamp,which connects to the upright portions, is placed over the rod to lockit in place. Polyaxial designs are similar, but the connection betweenthe head and the screw allows the head to twist and rotate relative tothe bone screw.

Open-head polyaxial and monaxial screws suffer from certainshortcomings. The size of the head scales with the size of the bonescrew. In situations that call for a larger screw, the surgeon may needto make more or larger incisions to accommodate the larger profile ofthe open-head screw. Conversely, if the surgeon will not or cannotenlarge the incision, he may instead use a smaller screw that may nothave the strength necessary for the particular application at hand. Inaddition, smaller polyaxial screws, with their smaller heads, may beable to achieve greater relative angles between the head and the screwthan larger screws. This is another reason a surgeon might select asmaller screw that may not be perfectly suited for the particular taskat hand. Furthermore, having to maintain stocks of screws and heads in avariety of sizes is cumbersome, costly, and error-prone.

Accordingly, there is a need for low-profile, high-strength polyaxialand monaxial bone screws.

SUMMARY OF THE PRESENT DISCLOSURE

The present disclosure meets the foregoing need using a closed-headdesign, which results in a significant reduce in size withoutcompromising strength, and other advantages apparent from the discussionherein.

Accordingly, one aspect of the present disclosure describes aclosed-head polyaxial screw that includes a set screw, a bone screw, aclosed head, a clamp, and a wedge. The closed head has an upper aperturethat is structured to receive the set screw. The closed head also has alower aperture that is structured to receive the bone screw. The clampis structured and located to retain the bone screw in the lower apertureof the closed head. The wedge is structured and located to seat theclamp in the lower aperture.

The bone screw may have a head, and the clamp may be structured andlocated to interface with the head of the bone screw in the loweraperture. The outer surface of the head of the bone screw may betextured, the inner surface of the clamp may be textured, or bothsurfaces may be textured. The bone screw may include dual bone threads.The closed head may be structured to receive a rod oriented at any oneof a number of angles relative to the bone screw. The set screw may beconfigured to retain the rod within the closed head, and the set screwmay press the rod against the wedge. The wedge may have a cutoutconfigured to receive the rod. The set screw may include a lip that isstructured and arranged to contact at least a portion of the closedhead, thereby retaining the set screw in the upper aperture.

According to another aspect of the present disclosure, a closed-headpolyaxial screw includes a set screw, a bone screw, a closed head, and aclamp. The closed head is integrally formed or constructed as one piecewith the bone screw. The closed head includes an upper aperture that isstructured to receive the set screw. The clamp is structured to bepositioned within the closed head.

The closed head may be structured and arranged to receive a rod orientedat one or more angles, which may be selectable from a plurality ofangles, relative to the bone screw. The set screw is structured andarranged to compress the clamp, thereby causing the clamp to retain therod within the closed head. The set screw may include an indentationstructured and arranged to interface with the clamp. The closed head mayinclude an orientation tab that is structured and arranged to properlyorient the clamp within the closed head. The clamp may have asubstantially circular shape or a substantially spherical shape. Thebone screw may include dual bone threads.

In yet another aspect of the present disclosure, a closed-head monaxialscrew includes a set screw, a bone screw, a closed head, and a clamp.The closed head is integrally formed or constructed as one piece withthe bone screw. The closed head includes an upper aperture that isstructured and arranged to receive the set screw. The clamp isstructured to be positioned under the set screw. The bone screw mayinclude dual bone threads. The closed head may be structured andarranged to receive a rod.

Additional features, advantages, and aspects of the present disclosuremay be set forth or apparent from consideration of the followingdetailed description, drawings, and claims. Moreover, it is to beunderstood that both the foregoing summary of the present disclosure andthe following detailed description are exemplary and intended to providefurther explanation without limiting the scope of the present disclosureas claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the present disclosure, are incorporated in andconstitute a part of this specification, illustrate aspects of thepresent disclosure and together with the detailed description serve toexplain the principles of the present disclosure. No attempt is made toshow structural details of the present disclosure in more detail thanmay be necessary for a fundamental understanding of the presentdisclosure and the various ways in which it may be practiced. In thedrawings:

FIG. 1 shows a cutaway view of a closed-head polyaxial screw, accordingto an aspect of the present disclosure;

FIG. 2 shows a closed-head polyaxial screw, according to an alternateaspect of the present disclosure;

FIG. 3 shows a closed-head polyaxial screw according to a further aspectof the present disclosure;

FIG. 4 shows a perspective view of the closed-head polyaxial screw ofFIG. 3; and

FIG. 5 shows a closed-head monaxial screw according to an aspect of thepresent disclosure.

FIG. 6 shows a closed-head monoaxial screw according to another aspectof the present disclosure.

FIG. 7 shows a closed-head polyaxial screw according to the presentdisclosure.

DETAILED DESCRIPTION OF THE PRESENT DISCLOSURE

The aspects of the present disclosure and the various features andadvantageous details thereof are explained more fully with reference tothe non-limiting aspects and examples that are described and/orillustrated in the accompanying drawings and detailed in the followingdescription. It should be noted that the features illustrated in thedrawings are not necessarily drawn to scale, and features of one aspectmay be employed with other aspects as the skilled artisan wouldrecognize, even if not explicitly stated herein. Descriptions ofwell-known components and processing techniques may be omitted so as tonot unnecessarily obscure the aspects of the present disclosure. Theexamples used herein are intended merely to facilitate an understandingof ways in which the present disclosure may be practiced and to furtherenable those of skill in the art to practice the aspects of the presentdisclosure. Accordingly, the examples and aspects herein should not beconstrued as limiting the scope of the present disclosure, which isdefined solely by the appended claims and applicable law. Moreover, itis noted that like reference numerals represent similar parts throughoutthe several views of the drawings.

FIG. 1 shows a cutaway view of a closed-head polyaxial screw 1000according to an aspect of the present disclosure. The screw 1000 mayinclude a bone screw 1100, a closed head 1200, a set screw 1300, a wedge1400, and one or more clamps 1500. The closed head 1200 may include alower aperture 1201, an upper aperture 1202, and a rod receivingaperture 1204. The rod receiving aperture 1204 may include an arch-shapewith a semicircular top and vertical sides. This shape may present amaximum area, indicated by the semicircular top, for a rod passingthrough or being retained within the screw 1000. For example, the rodmay be moved toward the bone screw 1100 when the closed head 1200 isaffixed to the rod, such as, e.g., by tightening the set screw 1300 ontothe rod. The closed head 1200 may include a second rod receivingaperture 1204 so that a rod (not shown) may pass completely through thehead 1200 rather than terminating in it.

The set screw 1300 may be introduced into the closed head 1200 throughthe lower aperture 1201. The upper aperture 1202 may be fitted withreceiving threads 1203 for mating to threads 1302 on the set screw 1300.The set screw threads 1302 may be threaded onto the receiving threads1203. The set screw 1300 may include a retaining lip 1303 or othermodification (not shown) to prevent the set screw 1300 from beingremoved through the upper aperture of the closed head 1200. The lip 1303may contact a rim or slope 1205 around the upper aperture 1202 toprevent the set screw 1300 from being threaded completely through theaperture 1202. The polyaxial screw 1000 may alternatively be structuredto have the set screw 1300 threaded in from the top of the upperaperture 1202. These screws may have a lip 1303 to prevent the set screw1300 from being threaded out the bottom of the aperture 1202 and intothe middle of the closed head 1200.

The set screw 1300 may include a receiving socket 1301 for a tool, suchas, e.g., a screw driver, a torx wrench, an allen wrench, a hex wrench,a socket driver, or the like. The base of the socket 1301 may include arim 1304. When a tool (not shown) is inserted into the socket 1301, therim 1304 may prevent the tool from being inserted past the set screw1300 and into the interior space of the closed head 1200. When a rod(not shown) is inserted into or through the closed head 1200, the rimmay prevent the tool from contacting and possibly damaging the rod. Therim 1303 may also define a cutout or hole 1305 at the center of the setscrew. The cutout 1305 may be circular, hexagonal, or any otherappropriate shape, and the cutout 1305 may allow a surgeon or other userof the polyaxial screw 1000 to view the progress of a rod as the rod isinserted into or through the closed head 1200.

The wedge 1400 may be inserted into the closed head 1200 through thelower aperture 1201 and pushed towards the upper aperture 1202. Thewedge 1400 may include a groove 1401 that may mate to a ring 1206located in the closed head 1200. The groove 1401 and the ring 1206 mayinteract to position and/or orient the wedge 1400 during assembly of thepolyaxial screw 1000. The groove 1401 and the ring 1206 may also bestructured to prevent the wedge 1400 from rising or being pushed abovethe point where the ring 1206 fits into the groove 1401. The wedge 1400may include a cutout 1402, which may have a rounded shape. The cutout1402 may mate to or receive a rod (not shown) inserted through theaperture 1204. For example, the rod may be pressed down into the cutout1402 by the set screw 1300. The pressure or force of the rod on thewedge 1400 may seat the wedge 1400 onto one or more clamps 1500. Thewedge 1400 may also transfer force or pressure to the clamps 1500,thereby increasing the pressure or friction of the interface between theclamps 1500 and the bone screw 1100, as discussed below.

One or more clamps 1500 may be inserted into the closed head 1200through the lower aperture 1201. Each clamp 1500 may be circular, or itmay occupy only a portion of the circumference of, e.g., the head of thebone screw 1100. For example, each clamp 1500 may be semicircular, oreach may represent one-third of a circle, as seen in FIG. 1. The clamps1500 may be centered or positioned so that they form a ring or circle.The clamps 1500 may then be pushed or moved towards the upper aperture1202. A top tapered surface 1501 on each clamp may contact a taperedshoulder 1207 within the closed head 1200. As the clamps 1500 are pushedfrom below, the angle of the surface 1501 and/or the shoulder 1207 maycause the clamps 1500 to angle in toward each other. The clamps 1500 maycome to a stop once each clamp 1500 comes into contact with anotherclamp 1500. This configuration and procedure may produce a wider openingat the bottom of the clamps 1500 than may be possible without thetapered surface 1501, tapered shoulder 1207, or both.

A bone screw 1100 may be inserted into the closed head 1200 through thelower aperture 1201. The bone screw 1100 may be inserted once the wedge1400 and clamps 1500 are in position, so that the head 1102 of the bonescrew may be surrounded by the clamps 1500 inside the closed head 1200.The bone screw 1100 may be manipulated or adjusted to ensure that theclamps 1500 are centered or properly positioned around the head 1102.Once the clamps 1500 are in position, the bone screw 1100 may be movedlower in the closed head 1200, which may seat the clamps 1500 lower inthe head 1200, such as, e.g., seen in FIG. 1.

The position and orientation of the closed head 1200 may be adjusted bypressing the head 1200 along its longitudinal axis in the direction ofthe bone screw 1100, or moving the bone screw 1100 along thelongitudinal axis of the closed head 1200 in the direction of the setscrew 1300. This motion may loosen the connection between the head 1102of the bone screw 1100 and the clamps 1500. With the clamps 1500loosened, the closed head 1200 may be rotated, twisted, or movedrelative to the bone screw 1100. Once the closed head 1200 is properlypositioned, the connection between the head 1200 and the bone screw 1100may be tightened by moving the closed head 1200 along its longitudinalaxis in a direction away from the bone screw 1100, or moving the bonescrew 1100 along the longitudinal axis of the closed head 1200 in adirection away from the set screw 1300.

The connection may be further strengthened or tightened by moving thewedge 1400 toward or onto the clamps 1500. The wedge may be moved towardthe clamp(s) 1500 by, for example, compression. For example, a tool orother instrument (not shown) may be inserted through the rod receivingaperture 1204 and used to compress the wedge 1400. The force of the toolmay be supplemented by rotating the set screw 1300 to further compressthe tool and the wedge 1400. Similarly, a rod (not shown) may beinserted through the aperture 1204. The set screw 1300 may be used tohold the rod in place. Since the aperture 1204 is arch-shaped, acounter-force to the set screw 1300 may not be provided by the closedhead 1200. Instead, the counter-force may be supplied by the wedge 1400,which may be supported by the clamps 1500 and the head 1102 of the bonescrew 1100. Thus, using the set screw 1300 to lock a rod in position inthe closed head 1200 may also lock the orientation of the closed head1200 relative to the bone screw 1100.

The inner surface 1502 of one or more clamps 1500 may be textured orpatterned, and the outer surface 1103 of the head 1102 of the bone screw1100 may likewise be textured or patterned. The texture or pattern mayinclude ribs, ridges, grooves, cross-hatching, or the like. The textureor pattern on the inner surface 1502 may be complementary to the textureor pattern on the outer surface 1103. The texture or pattern on theinner surface 1502, the outer surface 1103, or both may act to improvethe strength of the interface between the clamps 1500 and the head 1102of the bone screw 1300, for example, by increasing the friction betweenthe two surfaces. A stronger interface between the clamps 1500 and thehead 1102 of the bone screw 1300 may result in a stronger connectionbetween the bone screw 1300 and the closed head 1200, which in turn mayimprove the overall strength and stability of the spinalinstrumentation.

The bone screw 1100 may include a receiving socket 1101 for receiving atool, such as, e.g., a screw driver, a torx wrench, an allen wrench, ahex wrench, a socket driver, or the like. The socket 1101 may be sizedso that a tool (not shown) may be inserted through the cutout 1305 inthe set screw 1300 to actuate the bone screw 1100. As an alternativemeans of actuating or rotating the bone screw 1100, e.g., into bone, thescrew 1100 may be locked relative to the closed head 1200 as describedabove, then a special tool (not shown) may interface with the closedhead 1200 and rotate the head 1200, thereby rotating the screw 1100. Thetool may also interface with both the closed head 1200 and the bonescrew 1100. As a third option, the bone screw 1100 may be inserted intoa suitable site, e.g., a vertebral pedicle. The closed head 1200 may beassembled with the set screw 1300, wedge 1400, and clamps 1500 andattached to the screw 1100 once the screw 1100 is in position. Thistechnique may make it easier for a surgeon to properly insert the screw1100 into the site. With this technique, the screw 1100 may be fixed inplace, and the other components of the polyaxial screw 1000 may moverelative to it. For example, when it is described that the bone screw1100 may be inserted into the lower aperture 1201, this motion isrelative. It should be understood that the screw 1100 may be fixed inposition, and the aperture 1201 may be fitted over or onto the screwhead 1102. This distinction will be clear and easily understood by thoseskilled in the art.

The bone screw 1100 may include one or more bone threads. For example,the screw 1100 may have dual bone threads (as seen, e.g., in FIGS. 4 and5). Dual bone threads may increase the purchase of the screw in bothcortical bone and cancellous bone. The increased purchase may, in turn,reduce or substantially eliminate toggling, loosening, or pulling out ofthe bone screw 1100.

FIG. 2 shows a closed-head polyaxial screw 1000 according to analternate aspect of the present disclosure. The rod receiving aperture1204 may be circular, and the wedge 1400 may have a flat upper surface.The wedge 1400 may overlap with the aperture 1204, so that inserting arod (not shown) through the aperture 1204 may apply pressure to thewedge 1400 or force the wedge 1400 in the direction of the clamp(s)1500. A force or pressure on the wedge 1400 may be passed to one or moreclamps 1500, thereby increasing the pressure or friction of theinterface between the clamps 1500 and the bone screw 1100. A set screw1300 may be tightened onto a rod (not shown) inserted through the closedhead 1200 to affix the closed head 1200 to the rod.

FIG. 3 shows a closed-head polyaxial screw 2000 according to a furtheraspect of the present disclosure. The polyaxial screw 2000 may include aclosed head 2200, which may be integrally formed with a bone screw 2100,a set screw 2300, and a clamp 2500. The closed head 2200 and the bonescrew 2100 may be formed as one piece. The closed head may include anupper aperture 2202, as well as an aperture 2204 for receiving a rod orsimilar structure (not shown).

The set screw 2300 may include threads 2302. The set screw 2300 may beinserted into the aperture 2204. The set screw 2300 may be threaded ontoreceiving threads 2203 in the upper aperture 2202. The set screw 2300may include a retaining lip 2303. As the set screw 2300 is threaded awayfrom the bone screw 2100, through the upper aperture 2202, the lip 2303may contact a rim or slope 2205 around the upper aperture 2202. Theinteraction between the lip 2303 and the rim 2205 may prevent the screw2300 from being threaded out of the upper aperture 2202. The undersideof the set screw 2300 may include an indentation 2306 that may becontoured to contact or mate with a clamp 2500, as discussed below.

The clamp 2500 may be inserted into the closed head 2200 by placing theclamp 2500 in a flat or sideways orientation and passing it through theaperture 2204. Once inside the closed head 2200, the clamp 2500 may berotated or twisted into position. Proper positioning of the clamp 2500may be assisted by an orientation tab 2208 located inside the closedhead 2200, as seen, e.g., in FIG. 3. For example, the orientation tab2208 may fit into an orientation gap 2504 in the clamp 2500. The clamp2500 may include a circular, semi-circular, semi-spherical, or the like,shape. The clamp 2500 may include, for example, a c-clamp, or the like.The clamp 2500 may define a central opening 2503. The opening 2503 mayhave a shape that is circular, square, hexagonal, or the like, or anycombination thereof. For example, the opening 2503 is seen in FIG. 3 ashaving an upper portion that may be square and a lower portion that maybe circular. The clamp 2500 may be made of a biocompatible material. Itmay be somewhat soft and pliable, or it may be relative rigid.

The polyaxial screw 2000 may be inserted into bone using standardsurgical techniques. A special tool may be used to drive the screw 2000,and the closed head 2200 may include one or more attachment points,sockets, or receivers 2209 for such a tool. A rod (not shown) may beinserted into the rod receiving aperture 2204 and through the opening2503 in the clamp 2500. The set screw 2300 may the threaded toward oronto the clamp 2500, thereby compressing the clamp 2500. Thiscompression may cause the clamp 2500 to change shape and make theopening 2503 smaller. For example, the set screw 2300 and theindentation 2306 may cause the top portion of the clamp 2500 to slidearound the orientation gap 2504 until it abuts the orientation tab 2208.As the set screw 2300 continues to descend, the bottom portion of theclamp 2500 may slide into the orientation gap 2504 until it also abutsthe orientation tab 2208. This controlled collapse of the clamp 2500 maybe assisted by a cutout 2505 on the opposite side of the clamp 2500 fromthe orientation gap 2504.

The aperture 2204 and the clamp 2500 may be able to accommodate rodsthat are not perfectly perpendicular to the closed head 2200. Forexample, the clamp 2500 may be made of a more flexible material, and theopening 2503 may be wider that the rod. As the set screw 2300 isthreaded toward or onto the clamp 2500, the clamp 2500 may be compressedand close around the rod and at least partially conform to the shape ofthe rod, thereby increasing the friction or otherwise strengthening theinterface between the clamp and the rod. Additionally or alternatively,the outside of the clamp 2500 may be roughly circular, spherical, orcylindrical in shape, and it may be located in a substantially circularor spherical chamber within the closed head 2200. The clamp 2500 may bemade of a substantially rigid material. As the set screw 2300 isthreaded toward or onto the clamp 2500, the clamp 2500 may twist androtate so that the opening 2503 is better aligned with the rod. As theclamp 2500 tightens around the rod, more of its surface may be incontact with the rod, thereby increasing the friction or otherwisestrengthening the interface between the clamp and the rod.

FIG. 4 shows a perspective view of the closed-head polyaxial screw 2000.The bone screw portion 2100 of the screw 2000 may include one or morebone threads 2104. For example, screws of the present disclosure mayhave two or more threads around their outer diameter. The use ofmultiple threads may improve the purchase of the screw in both corticaland cancellous bone, which may in turn reduce or substantially eliminatetoggle and/or pull-out of the screw 2000.

Closed-head polyaxial screws of the present disclosure may offer one ormore additional advantages. For example, a closed-head screw may besmaller than a comparable open-head design. A smaller size may make thescrew more compatible with minimally invasive surgery techniques, suchas, e.g., requiring a smaller incision. The lower aperture 1201 mayaccommodate bone screws 1100 of different sizes, or bone screws ofdifferent sizes may all be manufactured with heads 1102 that arecompatible with the lower aperture 1201. Accordingly, only one size ortype of closed head 1200 may need to be manufactured, which may resultin lower manufacturing costs. Those savings may be passed on tohealthcare providers and ultimately patients. A constant size of theneck 1105 and lower aperture 1201, regardless of screw size, may enablethe possible angles between the closed head 1200 and the screw 1100 tobe the same across all sizes of screw 1100. Possible angles betweenpolyaxial screw 2000 and a rod (not shown) may likewise not be affectedthe by size of the bone screw 2100. By eliminating relative angle as acriterion for selecting screw size, polyaxial screws of the presentdisclosure may allow surgeons to select screws based on medical criteriarather than characteristics of the screw itself. Since polyaxial screw1000 employs a bottom-loading design, the design may be used to makeclosed-head polyaxial hooks. The necessary changes and modificationswill be apparent to those skilled in the art without departing from thespirit and scope of the present disclosure.

FIG. 5 shows a closed-head monaxial screw 3000 according to an aspect ofthe present disclosure. The monaxial screw 3000 may include a bone screw3100 integrally formed with a closed head 3200. The bone screw 3100 andthe closed head 3200 may be formed using one-piece construction. A setscrew 3300 may be located in the closed head 3200. The bone screw 3100and the closed head 3200 may be connected by a neck 3105. The bone screw3100 may have a plurality of threads, which may offer greater purchaseand stability in both cortical and cancellous bone. Greater purchase andstability may reduce or substantially eliminate toggling and/or pullingout of the monaxial screw 3000. For example, the bone screw may havedual bone threads 3104 a, 3104 b, as seen in FIG. 5.

The closed head 3200 may include a rod receiving aperture 3204 and anupper aperture 3202. The set screw 3300 may be introduced through therod receiving aperture 3204 and then threaded onto receiving threads3203 in the upper aperture 3202. The receiving threads may mate withthreads 3302 located on the outer surface of the set screw 3300. The setscrew may include a lip 3303 that may contact a rim 3205 around theupper aperture. Interaction between the lip 3303 and the rim 3205 mayprevent the set screw 3300 from being threaded out of the upper aperture3202. The set screw 3300 may also include a socket 3301 for receiving atool, such as, e.g., a screw driver, a torx wrench, an allen wrench, ahex wrench, a socket driver, or the like.

The monaxial screw 3000 may be inserted into bone using standardsurgical techniques. A special tool may be necessary or provided to gripthe closed head 3200 of the screw 3000 and twist the head 3200 to drivethe screw 3000 into the bone. Once the monaxial screw 3000 is positionedin bone, a rod (not shown) may be inserted through the aperture 3204 inthe head 3200. To affix the screw 3000 to the rod, a tool may beinserted into socket 3301 to rotate, thread, or drive the set screw 3300towards the rod. The set screw 3300, in turn, may engage the rod. Theset screw 3300 may include a rod interface surface 3307 made of a moreflexible, biocompatible material. As the set screw 3300 is drivenfurther and applies greater pressure to the rod, the surface 3307 mayconform to the shape of the rod, resulting in a greater area of contactbetween the surface 3307 and the rod. The greater contact area, in turn,may increase the friction or strength of the interface between thesurface 3307 and the rod.

The closed head design of the monaxial screw 3000 may result in asmaller size with fewer moving parts than an equivalent open-head screw.A smaller size may be more compatible with minimally invasive surgerytechniques, e.g., by allowing a surgeon to use a smaller incision. Thedual bone threads 3104 a, 3104 b, combined with a larger neck 3105relative to the shank size, may provide more secure fixation to bonethan with previous and/or open-head designs. More secure fixation mayinclude, e.g., reduced or substantially eliminated chance of pullout,toggling, breakage, or other disruption of the connection between thescrew 3000 and bone to which it is attached. In addition, the size ofthe closed head 3200 may remain constant while the diameter of the bonescrew 3100 may vary, which may enable common instrumentation for allscrew sizes. Common instrumentation may make surgical procedures fasterand simpler. Furthermore, common instrumentation may reducemanufacturing and shipping costs, and these savings may be passed on tomedical professionals and ultimately patients.

FIGS. 6 and 7 illustrate another embodiment of the present invention.FIG. 6 shows a closed-head monoaxial screw having the angled tulipportion of the screw. The angulation of the closed-head tulip allows forthe insertion of the elongate rod at an angle. FIG. 7 shows aclosed-head polyaxial screw having an angled closed head tulip that alsoallows the rod to be positioned at an angle rather than beingperpendicular to the head of the screw. It should be noted that althougha single angled closed head tulip is illustrated, any angle that issuitable can be manufacture to accommodate for use in the spine. Itshould be further noted that the set screw on the angled closed-headmono and polyaxial screws are also angled so that the rod may becaptured within optimally within the closed-head portion of the screw.

While the present disclosure has been described in terms of exemplaryaspects, those skilled in the art will recognize that the presentdisclosure can be practiced with modifications in the spirit and scopeof the appended claims. These examples given above are merelyillustrative and are not meant to be an exhaustive list of all possibledesigns, aspects, applications or modifications of the presentdisclosure.

What is claimed is:
 1. A closed-head monaxial screw comprising: a closedhead comprising an upper threaded portion having an upper aperture,wherein the head further comprises a lateral rod-receiving apertureconfigured to receive a rod, the head being closed such that a wall ofthe head is adapted to completely and circumferentially surround thelateral rod-receiving aperture around a longitudinal axis of the lateralrod-receiving aperture,. wherein the upper threaded portion isintegrally formed in the closed head; a bone screw connected to the headby a neck; and a set screw configured to be received in the upperaperture from only the rod-receiving aperture in the head and having aretaining lip extending laterally past the outermost diameter of aninternal threading of the upper aperture and adapted to directly contactan upper surface of the rod-receiving aperture such that the set screwis prevented from moving upwardly and out of the upper threaded portion,wherein the set screw includes a rod interface surface and the rodinterface surface is formed of a more flexible material relative toother portions of the set screw, wherein the head and the bone screw areformed as one piece and at a fixed angle.
 2. The closed-head monaxialscrew of claim 1, wherein the retaining lip is capable of contacting arim of the head member for preventing the set screw from moving upwardlyand out of the upper aperture of the head.
 3. The closed-head monaxialscrew of claim 1, wherein the lip is disposed at a lower end of the setscrew and is adapted to abut a rim of the upper threaded portion.
 4. Theclosed-head monaxial screw of claim 3, wherein the head comprises asocket configured for a tool.
 5. The closed-head monaxial screw of claim4, wherein the rod interface surface is configured to conform to theshape of rod upon an application of force by the set screw onto the rod.6. The closed-head monaxial screw of claim 5, wherein the rod interfacesurface is comprised of a biocompatible material.
 7. A closed-headmonaxial screw comprising: a head member including an upper threadedportion having an upper aperture, the head member further including alateral rod-receiving aperture for receiving a rod therein, the headmember being closed such that a wall of the head member is adapted tocompletely and circumferentially surround the lateral rod-receivingaperture around a longitudinal axis of the lateral rod-receivingaperture, wherein the upper threaded portion is integrally formed in thehead member; a neck; a bone screw connected to the head member via theneck; and a set screw received through the upper aperture in the headmember from only the rod-receiving aperture, wherein the set screwincludes a lip at its lower end and extending laterally past theoutermost diameter of an internal threading of the upper aperture so asto directly contact an inner lower end of the upper threaded portion soas to prevent the set screw from moving upwardly and out of the upperthreaded portion in the head member, wherein the set screw includes arod interface surface and the rod interface surface is formed of a moreflexible material relative to other portions of the set screw, whereinthe head member, the neck and the bone screw are formed as one piece andat a fixed angle.
 8. The closed-head monaxial screw of claim 7, whereinthe head member and the bone screw are integrally formed as one piece.9. The closed-head monaxial screw of claim 7, wherein the lip isconfigured to contact a rim of the head member for preventing the setscrew from moving upwardly and out of the aperture of the head member.10. The closed-head monaxial screw of claim 7, wherein the lip of theset screw is adapted to abut a rim of the upper threaded portion. 11.The closed-head monaxial screw of claim 10, wherein the head membercomprises socket configured for a tool.
 12. The closed-head monaxialscrew of claim 11, wherein the rod interface surface is configured toconform to the shape of rod upon an application of force by the setscrew onto the rod.
 13. The closed-head monaxial screw of claim 12,wherein the rod interface surface is comprised of a biocompatiblematerial.